In recent years, along with miniaturization of a semiconductor device, a wiring layer including wiring, a plug, and the like formed in the semiconductor device has been increasingly fine. Along with this, a planarization technique through chemical mechanical polishing (hereinafter may be called “CMP”) has been used for the wiring layer. As such technique, there is known, for example, a damascene process involving depositing a conductive metal, such as aluminum, copper, or tungsten, in a fine trench or hole formed in an insulating film made of silicon oxide or the like on a semiconductor substrate by a method such as sputtering or plating, and then removing an excessively deposited metal film by CMP to leave the metal only in the fine trench or hole portion (see, for example, Patent Literature 1).
In this process, tungsten, which is excellent in embedding property, is used as a material particularly for, for example, a plug to electrically connect wires to each other in an upper and lower vertical direction. In chemical mechanical polishing for forming the tungsten plug, a first polishing treatment step of mainly polishing a tungsten layer formed on an insulating film, and a second polishing treatment step of polishing the tungsten plug, a barrier metal film made of titanium or the like, and the insulating film are sequentially performed.
With regard to such chemical mechanical polishing of the tungsten layer and the tungsten plug (hereinafter may be called “tungsten film”), for example, in Patent Literature 2, as a semiconductor polishing composition to be used in a stage before finishing polishing corresponding to the first polishing treatment step, there is a disclosure of a semiconductor polishing composition that is intended to provide a high polishing rate and prevent surface roughening of a wafer surface after polishing due to high reactivity between an amine compound serving as a polishing accelerator and silicon, and that contains: abrasive grains, such as colloidal silica; a basic low-molecular-weight compound, such as an amine compound; and a water-soluble polymer compound containing a nitrogen-containing group, such as polyethyleneimine.
In addition, in Patent Literature 3, there is a disclosure of a chemical mechanical polishing method for a substrate containing tungsten, involving performing polishing using a chemical mechanical polishing composition containing: a tungsten etchant, such as an oxidizing agent; an inhibitor of tungsten etching, which is a specific polymer or the like containing a nitrogen atom, and is present in an amount of from 1 ppm to 1,000 ppm; and water. The chemical mechanical polishing composition to be used in this polishing method may contain, as optional components, an abrasive, such as colloidal silica, and compounds such as monopersulfates (SO52−) and dipersulfates (S2O82−).
Meanwhile, along with extremely high integration of the semiconductor device in recent years, even contamination with an extremely small amount of impurities has largely affected the performance of the device, and by extension, a product yield. For example, on the surface of an uncleaned 8-inch wafer after completion of CMP, the number of particles each having a diameter of 0.2 μm or more to be counted is 10,000 or more, and there is a demand for removal of the particles to several to dozens of pieces through cleaning. In addition, the concentration of metal impurities (the number of impurity atoms per square centimeter) on the surface is from 1×1011 to 1×1012 or more, and there is a demand for removal of the metal impurities to 1×1010 or less through the cleaning. Therefore, when CMP is introduced in the production of the semiconductor device, the cleaning after CMP is an inevitable and essential step.
Further, in an advanced node semiconductor substrate in which the tungsten layer and the tungsten plug are miniaturized, the wiring and the plug each have a size of from about several tens to about a hundred and several tens of tungsten atoms in width or diameter, and hence generation of even a fine pit at an atomic level having a diameter equivalent to several tens of tungsten atoms causes severe electrical characteristic failure. Therefore, recently, in any of a finishing polishing step (so-called polishing step), a cleaning step on a platen after polishing, and a post-cleaning step in a cleaning apparatus, there has emerged a need for a corrosion suppression technology for preventing the tungsten film from being eluted at the atomic level (see, for example, Patent Literature 4).